A radial-flow heat-dissipating fan includes a casing and a cover mounted to a side of the casing. The casing includes a compartment and a side air outlet, and the cover includes an air inlet. A primary fan wheel is rotatably mounted in the compartment and the primary fan wheel includes a hub and a plurality of radial-flow blades surrounding the hub. An auxiliary fan wheel is mounted in the air inlet of the cover and includes a plurality of axial-flow blades. An airflow transition area is defined between a circumference of the hub of the primary fan wheel, the radial-flow blades, and the axial-flow blades. The axial-flow blades increase axial inlet airflow via the air inlet, with the airflow transition area changing a direction of the axial inlet airflow into centrifugal airflow that is outputted via the side air outlet by the radial-flow blades.